London: Thousands of people suffering from common forms of blindness could have their sight restored by a pioneering treatment. Researchers at Oxford University have discovered that by replacing a missing protein in the retina they can prevent cells from degenerating.
The therapy even improves the sight of those who have already begun to go blind in results that have "surpassed expectations".
Two men who were already at an advanced stage of vision loss have experienced "dramatic improvements" in their sight which, so far, have lasted for two years.
Professor Robert MacLaren, of the Nuffield Laboratory of Ophthalmology at the University of Oxford, said: "We're absolutely delighted with the results so far. In truth, we did not expect to see such dramatic improvements This has huge implications for anyone with a genetic retinal disease such as age-related macular degeneration or retinitis pigmentosa because it has, for the first time, shown, that gene therapy can be applied safely before the onset of vision loss."
The trial was carried out on patients suffering from choroideremia - a rare inherited cause of blindness which affects about one in 50,000 people.
It is caused by a defective gene which fails to produce REP-1 - a protein needed to keep pigment cells in the retina healthy. Without it the cells slowly stop working, switch off and die. The first symptom of the condition is usually poor night vision which can occur in early childhood. Later, the field of vision progressively narrows to a "tunnel" until only a small central slit remains.
The scientists found that the protein could be replaced in the eye by inserting it into the DNA of a harmless virus which can be injected into cells beneath the retina. As the virus "infects" these retinal cells the missing protein is restored.
"The purpose of our trial is to put this missing protein back into the retinal cells and prevent further degeneration," said Professor MacLaren.
"We're not talking about treatment that needs to be repeated; we're talking about a single one-off replacement of the gene.
"What was unique and exciting is we noticed visual improvements very early, which shows us that it is working.
"If we were able to treat people early, get them in their teens or late childhood, we'd be getting the virus in before their vision is lost. If the treatment works, we would be able to prevent them from going blind."
Jonathan Wyatt, 65, a barrister from Bristol, was the first patient to be treated, in 2012. He said: "The very next day after the operation I looked at a mobile phone that my wife Diana had and I could read the digits. I hadn't been able to read the digits on a mobile phone for five years."
Wayne Thompson, 43, an IT project manager from Staffordshire, was treated in April last year with a higher dose of the gene therapy as part of a subsequent trial.
"One night in the summer, my wife called me outside as it was a particularly starry evening. As I looked up I was amazed that I was able to see a few stars. I hadn't seen stars for a long, long time."
Professor Miguel Seabra, whose research at Imperial College London identified the protein involved in choroideremia, said: "My team has spent 20 years trying to understand choroideremia and develop a cure, so to finally see the rewards reaching patients is extremely gratifying."
A third of the diseases which affect the eyes are genetic in origin. In Britain one in 20 people over 65 suffers from macular degeneration.
The results are published in The Lancet.